1. Field of the Invention
The present invention relates to a process for producing a highly purified Stevioside and Rebaudioside A from the extract of the Stevia rebaudiana Bertoni plant and use thereof in various food products and beverages.
2. Description of the Related Art
In view of food sanitation, the use of artificial sweeteners such as dulcin, sodium cyclamate and saccharin has been restricted. However natural sweeteners have been receiving increasing demand. Stevia rebaudiana Bertoni is a plant that produces an alternative sweetener that has an added advantage of being a natural plant product. In addition, the sweet steviol glycosides have functional and sensory properties superior to those of many high potency sweeteners.
The sweet diterpene glycosides of Stevia have been characterized, and eight sweet glycosides of steviol have been identified. These glycosides accumulate in Stevia leaves where they may attain from 10 to 20% of the leaf dry weight. On a dry weight basis, a typical profile for the four major glycosides found in the leaves of Stevia includes 0.3% dulcoside, 0.6% Rebaudioside C, 3.8% Rebaudioside A and 9.1% Stevioside. Other glycosides identified within Stevia include Rebaudioside B, C, and E, and dulcosides A and B. Rebaudioside B may be an artifact formed from Rebaudioside A during extraction, since both Rebaudioside A and Rebaudioside D are found to convert to Rebaudioside B by alkaline hydrolysis.
Out of four major diterpene glycoside sweeteners present in Stevia leaves only two (Stevioside and Rebaudioside A) have physical and sensory properties that are well characterized. Stevioside and Rebaudioside A were tested for stability in carbonated beverages and found to be both heat and pH stable (Chang and Cook, 1983). Stevioside is known to be 110 to 270 times sweeter than sucrose, Rebaudioside A between 150 and 320 times sweeter than sucrose, and Rebaudioside C between 40 and 60 times sweeter than sucrose. Dulcoside A was found to be 30 times sweeter than sucrose (Phillips, 1989 and Tanaka, 1997).
However, apart from its high level of sweetness, they have also intrinsic properties of post-bitter taste and unpleasant and undesirable aftertaste. At present, the main method to improve the taste quality is the enzymatic modification of Stevioside or Rebaudioside A. On the other hand, some undesirable characteristics of glycosides can be as a result of contamination of other substances, presented in extract.
A process for the recovery of diterpene glycosides, including Stevioside from the Stevia rebaudiana plant is described (U.S. Pat. No. 4,361,697). A variety of solvents, having different polarities, were used in a sequential treatment that concluded with a high performance liquid chromatographic (HPLC) separation procedure.
A method for the recovery of Rebaudioside A from the leaves of Stevia rebaudiana plants has been developed (U.S. Pat. No. 4,082,858). Again, final purification is achieved by liquid chromatography subsequent to an initial extraction with water and an alkanol having from 1 to 3 carbon carbons, preferably methanol. It is also known that water may be used as the initial solvent; their preferred solvent at this stage is a liquid haloalkane having from 1 to 4 carbon atoms. The preferred second solvent is an alkanol having from 1 to 3 carbon atoms, while the preferred third solvent is an alkanol having from 1 to 4 carbon atoms and optionally minor amounts of water.
Individual sweet glycosides can be obtained from the Stevia rebaudiana plant. A mixture of sweet glycosides extracted from the Stevia rebaudiana plant are processed to remove impurities by using two types of ion-exchangers. After removing the mixed sweet glycosides from the second column with methanol, the solution is dried. Upon refluxing the dried solids in a methanol solution and then cooling the solution, Stevioside precipitates out. The filtrate is further concentrated and cooled to precipitate out Rebaudioside A. This Rebaudioside A can be further purified as can the previously obtained Stevioside (U.S. Pat. No. 5,962,678). However, a large amount of toxic organic solvent, such as methanol is used.
However, all the above-mentioned methods allow the production of not highly purified Stevioside and Rebaudioside A, which further possess a residual bitterness and aftertaste. The bitterness and aftertaste can be eliminated by intermolecular transglycosylation using various enzymes, upon which the attachment of new carbohydrates at positions C13 and C19 takes place. The number of carbohydrate units in the above-mentioned positions determines the quality and degree of that component's sweetness. The process of transglycosylation is described in U.S. Pat. Nos. 4,219,571; 4,590,160; 6,255,557).
On the other hand, highly purified Stevioside and Rebaudioside A can possess an improved taste profile. It is also important to unify the sweeteners specification, because at present in the market there are many types of Stevia based sweeteners with different specifications and ratio of glycosides.
As a result, there is a need to provide a commercially valuable process for the manufacturing the highly purified Stevioside and Rebaudioside A from the extract of the Stevia rebaudiana Bertoni plant, and use thereof in various beverages and food products.